.img {
    width: 500px;
    height: 500px;
    background-image: url(./imgs/1.jpg);
    position: relative;
}

.img .mask {
    position: absolute;
    left: 0;
    top: 0;
    width: 100px;
    height: 100px;
    background-color: yellow;
    opacity: .5;
    display: none;
}

.enlarge {
    width: 200px;
    height: 200px;
    background-image: url(./imgs/1big.jpg);
    background-repeat: no-repeat;
    background-position: 0 0;
    display: none;
}
